Generation of patterned radiation

ABSTRACT

Imaging apparatus includes an illumination assembly, including a plurality of radiation sources and projection optics, which are configured to project radiation from the radiation sources onto different, respective regions of a scene. An imaging assembly includes an image sensor and objective optics configured to form an optical image of the scene on the image sensor, which includes an array of sensor elements arranged in multiple groups, which are triggered by a rolling shutter to capture the radiation from the scene in successive, respective exposure periods from different, respective areas of the scene so as to form an electronic image of the scene. A controller is coupled to actuate the radiation sources sequentially in a pulsed mode so that the illumination assembly illuminates the different, respective areas of the scene in synchronization with the rolling shutter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/762,373, filed Apr. 19, 2010, which claims the benefit of U.S.Provisional Patent Application 61/300,465, filed Feb. 2, 2010, which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to systems and methods forelectronic imaging, and specifically to methods of illumination forenhancing the quality of captured images.

BACKGROUND OF THE INVENTION

Most low-cost CMOS image sensors use a rolling shutter, in whichsuccessive rows of sensor elements are triggered sequentially to capturelight. This method of image acquisition thus records each individualframe not as a single snapshot at a point in time, but rather as asequence of image stripes scanning across the frame. The result of therolling shutter is that not all parts of the optical image are recordedat exactly the same time (although the frame is stored as a singleelectronic image).

The use of a rolling shutter introduces a temporal shear in the imageframe, which can create artifacts in imaging of moving objects. Bradleyet al. address this problem in “Synchronization and Rolling ShutterCompensation for Consumer Video Camera Arrays,” IEEE InternationalWorkshop on Projector-Camera Systems—PROCAMS 2009 (Miami Beach, Fla.,2009), which is incorporated herein by reference. The authors propose tosolve the problem using synchronized stroboscopic illumination.

SUMMARY

Embodiments of the present invention that are described hereinbelowprovide apparatus and methods for illuminating an object that can beadvantageous when the object is imaged using a sensor with a rollingshutter.

There is therefore provided, in accordance with an embodiment of thepresent invention, imaging apparatus, including an illuminationassembly, including a plurality of radiation sources and projectionoptics, which are configured to project radiation from the radiationsources onto different, respective regions of a scene. An imagingassembly includes an image sensor and objective optics configured toform an optical image of the scene on the image sensor, which includesan array of sensor elements arranged in multiple groups, which aretriggered by a rolling shutter to capture the radiation from the scenein successive, respective exposure periods from different, respectiveareas of the scene so as to form an electronic image of the scene. Acontroller is coupled to actuate the radiation sources sequentially in apulsed mode so that the illumination assembly illuminates the different,respective areas of the scene in synchronization with the rollingshutter.

In disclosed embodiments, each group includes one or more rows of thesensor elements, and the regions define stripes that extend across thescene in a direction parallel to the rows. Typically, each stripeilluminates a respective region that contains the areas of the scenefrom which the sensor elements in a respective set of multiple rowscapture the radiation, and the controller is configured to actuate theradiation sources so that the projected radiation sweeps across thescene in a direction perpendicular to the rows.

In a disclosed embodiment, the rolling shutter defines a frame time forcapturing the entire electronic image, and the controller is configuredto actuate each of the radiation sources for a respective actuationperiod that is less than half the frame time. The controller may actuateeach of the radiation sources so that the illumination assemblyilluminates each area of the scene only during a respective exposureperiod of a corresponding group of the sensor elements that captures theradiation from the area.

In some embodiments, the projection optics include a patterning element,which is configured so that the radiation is projected onto the scene ina predefined pattern, which is detectable in the electronic image formedby the imaging assembly. Typically, the controller is configured toanalyze the pattern in the electronic image so as to generate a depthmap of the scene. In one embodiment, the radiation sources include amatrix of light-emitting elements, which are arranged on a substrate andare configured to emit the radiation in a direction perpendicular to thesubstrate. In another embodiment, the radiation sources include a row ofedge-emitting elements, which are arranged on a substrate and areconfigured to emit the radiation in a direction parallel to thesubstrate, and the illumination assembly includes a reflector disposedon the substrate so as to turn the radiation emitted by theedge-emitting elements away from the substrate and toward the patterningelement.

There is also provided, in accordance with an embodiment of the presentinvention, a method for imaging, including arranging a plurality ofradiation sources to project radiation onto different, respectiveregions of the scene. An image sensor, which includes an array of sensorelements arranged in multiple groups, is configured to receive anoptical image of the scene, in which the groups of the sensor elementsreceive the radiation from different, respective areas of the scene. Thegroups of the sensor elements are triggered with a rolling shutter tocapture the radiation from the scene in successive, respective exposureperiods so as to form an electronic image of the scene. The radiationsources are actuated sequentially in a pulsed mode so as to illuminatethe different, respective areas of the scene in synchronization with therolling shutter.

In one embodiment, configuring the image sensor includes arrangingmultiple image sensors, having respective rolling shutters, togetherwith multiple, respective pluralities of the radiation sources to formrespective electronic images of different, respective, overlapping partsof a scene, and actuating the radiation sources includes synchronizingthe respective pluralities of the radiation sources over the multipleimage sensors so as to control an overlap of the respective areas of thescene illuminated by the radiation sources at any given time. The methodmay include analyzing the pattern over the electronic images formed bythe multiple image sensors in order to generate a depth map of thescene.

There is additionally provided, in accordance with an embodiment of thepresent invention, imaging apparatus, including multiple imaging units.The imaging units include respective pluralities of radiation sourcesand projection optics, which are configured to project radiation fromthe radiation sources onto different, respective regions of a scene, andrespective imaging assemblies. The imaging assemblies include respectiveimage sensors and objective optics configured to form respective opticalimages of different, respective, overlapping parts of the scene on therespective image sensors. Each image sensor includes an array of sensorelements arranged in multiple groups, which are triggered by a rollingshutter to capture the radiation from the scene in successive,respective exposure periods from different, respective areas of thescene so as to form respective electronic images of the scene. Theradiation sources are actuated sequentially in a pulsed mode so that theillumination assembly illuminates the different, respective areas of thescene in synchronization with the rolling shutter, while synchronizingthe respective pluralities of the radiation sources over the multipleimage sensors so as to control an overlap of the respective areas of thescene illuminated by the radiation sources at any given time.

Typically, the overlap is controlled so that the respective areas of thescene illuminated by the radiation sources at any given time arenon-overlapping.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an imaging system, in accordance withan embodiment of the present invention;

FIG. 2 is a schematic representation of a portion of an image framecaptured using stripe illumination, in accordance with an embodiment ofthe present invention;

FIG. 3 is a timing diagram showing synchronization of stripeillumination with rolling shutter operation, in accordance with anembodiment of the present invention;

FIG. 4A is a schematic side view of a projection module, in accordancewith an embodiment of the present invention;

FIG. 4B is a schematic top view of an optoelectronic subassembly used inthe projection module of FIG. 4A;

FIGS. 5A and 5B are schematic side and top views, respectively, of anoptoelectronic subassembly, in accordance with another embodiment of thepresent invention;

FIG. 5C is a schematic pictorial view of a prism used in the subassemblyof FIGS. 5A and 5B;

FIG. 6 is a schematic side view of an illumination assembly, inaccordance with an alternative embodiment of the present invention;

FIG. 7 is a schematic representation of a portion of an image frameilluminated by the illumination assembly of FIG. 6;

FIG. 8 is a schematic side view of an imaging system, in accordance withanother embodiment of the present invention; and

FIG. 9 is a schematic pictorial view of an imaging system, in accordancewith yet another embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS Overview

Various types of imaging systems include optical projectors forilluminating the scene of interest. For example, a projector may be usedto cast a pattern of coded or structured light onto an object forpurposes of three-dimensional (3D) depth mapping. In this regard, U.S.Patent Application Publication 2008/0240502, whose disclosure isincorporated herein by reference, describes an illumination assembly inwhich a light source, such as a laser diode or LED, transilluminates atransparency with optical radiation so as to project a pattern onto theobject. (The terms “optical,” “light” and “illumination” as used hereinrefer generally to any of visible, infrared, and ultraviolet radiation.)An image sensor captures an image of the pattern that is projected ontothe object, and a processor processes the image so as to reconstruct athree-dimensional (3D) map of the object.

Systems based on projection of patterned light may suffer from lowsignal/background ratio due to limitations on the power of theprojector, particularly in conditions of strong ambient light.Embodiments of the present invention address this problem by projectingradiation onto the scene of interest in a synchronized spatial sweep,which is timed to take advantage of the rolling shutter of the imagesensor in order to improve the signal/background ratio of the system.

In embodiments of the present invention, the rolling shutter is operatedso as to cause different groups (typically successive rows) of sensorelements in the image sensor to capture radiation in different,successive exposure periods, which are much shorter than the total frameperiod (typically less than half, and possibly less than 10%). Each suchgroup collects radiation from a different, respective area of the scene,which is focused onto the image sensor by objective optics. Theillumination assembly is controlled so as to sweep the projectedradiation over those areas of the scene in synchronization with therolling shutter, so that each area of the scene is illuminated duringthe specific time that the corresponding group of sensor elements isactive. As a result, the output power of the illumination assembly isconcentrated, in each area of the scene, in the specific exposureperiods during which the corresponding sensor elements are able tocollect radiation from that area. Limitation of the exposure periods bythe rolling shutter reduces the total amount of ambient radiation thatis collected, without wasting any of the projected radiation. Therefore,the signal/background ratio of the system is enhanced substantially evenwithout increasing the average power of the illumination.

In the embodiments that are disclosed hereinbelow, the illuminationassembly comprises an array of radiation sources, with projection opticsthat project radiation from the radiation sources onto different,respective regions of the scene. The spatial sweep of the projectedradiation is accomplished by pulsing the radiation sources sequentially.The respective region of the scene that is illuminated by each radiationsource overlaps the areas in the scene that are sensed by one or more ofthe groups of the sensor elements. Each radiation source is thus pulsedon only during the time that the corresponding groups of sensor elementsare active. This sequential pulsed operation of the array of radiationsources provides full flexibility in choosing the optimal timing for thespatial sweep of radiation, as well as high reliability in that nomoving parts or active optical elements (other than the radiationsources themselves) are required to implement the sweep.

Although the embodiments that are described below relate specifically toprojection of patterned light in a 3D sensing system, the principles ofthe present invention may similarly be applied to enhance theperformance of other projection-based imaging systems. The rollingshutter in these embodiments is assumed to activate the sensor elementsin the image sensor row by row, as in conventional CMOS image sensorsthat are known in the art; but the principles of the present inventionmay similarly be applied in conjunction with image sensors that useother sorts of sequential activation of groups of sensor elements, suchas block-by-block activation.

System Description

FIG. 1 is a schematic side view of an imaging system 20, in accordancewith an embodiment of the present invention. A set of X-Y-Z axes is usedin this figure and throughout the description that follows to aid inunderstanding the orientation of the figures, wherein the X-Y plane isthe frontal plane of system 20, and the Z-axis extends perpendicularlyfrom this plane toward the scene. The choice of axes, however, isarbitrary and is made solely for the sake of convenience in describingembodiments of the invention.

An illumination assembly 22 projects a patterned radiation field 24 ontoan object 26 (in this case a hand of a user of the system) in a scene.An imaging assembly 28 captures an image of the scene within a field ofview 30. A controller 31 or other electronic processor processes theimage in order to generate a 3D depth map of object 26. Further detailsof this sort of mapping process are described, for example, in theabove-mentioned U.S. 2008/0240502 and in PCT International PublicationWO 2007/105205, whose disclosure is also incorporated herein byreference. The 3D map of the user's hand (and/or other parts of theuser's body) may be used in a gesture-based computer interface, but thissort of functionality is beyond the scope of the present patentapplication.

Imaging assembly 28 comprises objective optics 36, which form an opticalimage of the scene containing object 26 on an image sensor 38, such as aCMOS integrated circuit image sensor. The image sensor comprises anarray of sensor elements 40, arranged in multiple rows. The sensorelements generate respective signals in response to the radiationfocused onto them by optics 36, wherein the pixel value of each pixel inthe electronic images output by image sensor 38 corresponds to thesignal from a respective sensor element 40. The sensor elements areactivated and deactivated, row by row, by a rolling shutter, whosetiming is set by controller 31. This sort of rolling shutter operationis a standard feature of many CMOS image sensors.

Illumination assembly 22 comprises a projection module 32, whichgenerates a beam of patterned light, and projection optics 34, whichproject the beam onto field 24. Module 32 typically comprises multipleradiation sources, along with optics for pattern generation. Controller31 actuates the radiation sources sequentially, in a pulsed mode, insynchronization with the rolling shutter of image sensor 38. The designof module 32 and the synchronization of its operation with the rollingshutter are described in detail hereinbelow.

FIG. 2 is a schematic representation of a portion of an image frame 42captured by system 20, in accordance with an embodiment of the presentinvention. Frame 42 comprises a matrix of pixels 44, each correspondingto the signal generated by a corresponding sensor element 40 in imagesensor 38. Thus, each row of pixels 44 corresponds to the area in thescene from which radiation is captured by the corresponding row ofsensor elements.

Illumination assembly 22 generates multiple stripes 46, 48, 50, 52, . .. of illumination. Each such stripe is generated by a respectiveradiation source or group of radiation sources. (Example arrangements ofradiation sources that can be used to generate this sort of multi-stripeillumination are shown in the figures that follow.) The region definedby each stripe covers the area of a number of the rows of pixels 44. Inother words, each stripe illuminates a certain area of the scene fromwhich the image sensors in the corresponding rows capture radiation.Although stripes 46, 48, 50, 52 are shown in FIG. 2, for the sake ofsimplicity, as being precisely adjacent to one another andnon-overlapping, in practical systems there is generally a certainamount of overlap between the stripes in order to ensure that all areasof the scene are illuminated.

FIG. 3 is a timing diagram illustrating synchronization of the sort ofstripe illumination shown in FIG. 2 with the operation of a rollingshutter in image sensor 38, in accordance with an embodiment of thepresent invention. Traces 56 correspond to the operation of the rollingshutter on successive rows of sensor elements, wherein the elements areactive (i.e., convert received photons to electrons in the output signalfrom the image sensor) when the corresponding trace is high. The periodduring which a given row is active is referred to herein as the exposureperiod of that row. The exposure periods of successive rows arestaggered, so that each row is activated shortly after the precedingrow. The rows are arranged in groups 58, 60, . . . , each groupcorresponding to the region covered by one of stripes 46, 48, . . . .

Traces 62, 64, . . . correspond to actuation of the respective radiationsources that generate stripes 46, 48, . . . . In other words, when trace62 is high, the radiation source that generates stripe 46 is actuated,and so on. For each group 58, 60, . . . , of the rows, the actuationperiod of the corresponding radiation source is set so as to fallentirely within the exposure periods of all the rows in the group. Thus,the illumination assembly illuminates each area of the scene only duringthe exposure periods of the sensor elements that capture the radiationfrom the area, and none of the illumination is wasted.

Trace 64 goes high just as trace 62 goes low, and so forth over all theradiation sources in illumination assembly 22. Thus, the stripe outputof the illumination assembly sweeps across the scene in a sweepdirection perpendicular to the rows of pixels 44 (and sensor elements40), completing one such sweep in each image frame, in synchronizationwith the sweep of the rolling shutter of image sensor 38. The duty cycleof each radiation source is roughly 1:N, wherein N is the number ofstripes (each illuminated by a respective radiation source or group ofradiation sources). In the timing scheme of FIG. 3, the actuation periodof each illumination stripe is approximately 1/(N*FR), while theexposure period of each row of sensor elements 40 is approximately2/(N*FR), wherein FR is the frame rate, such as 30 frames/sec. Thesetiming relations typically make optimal use of the availableillumination power and provide the greatest possible enhancement ofsignal/background ratio.

Alternatively, other timing relations may be used between the framerate, actuation periods and exposure times. These alternative timingarrangements may be advantageous in situations in which the geometricalrelationships between illumination stripes and sensor rows are notmaintained as precisely as in FIG. 2, and particularly when successivestripes partially overlap.

Illumination Module With Edge Emitters

FIG. 4A is a schematic side view of illumination module 32, while FIG.4B is a schematic top view of an optoelectronic subassembly used inillumination module 32, in accordance with an embodiment of the presentinvention. Module 32 comprises a row of edge-emitting optoelectronicelements 70, such as laser diodes, which are formed on a substrate 72,such as a silicon wafer. (Only one of the elements can be seen in theside view of FIG. 4A.) Elements 70 emit radiation in a directionparallel to the substrate. A reflector 74 on the substrate turns theradiation emitted by elements 70 away from the substrate, which isoriented in the X-Y plane, toward the Z-axis. The reflector may beintegrally formed in substrate 72, as shown in FIG. 4A, or it mayalternatively comprise a separate element, which is positioned on thesubstrate and aligned with optoelectronic elements 70. Reflector 74 maysimply comprise a flat reflecting surface, or it may alternativelycomprise one or more curved surfaces or multiple flat surfaces in orderto spread or focus the radiation, as illustrated in FIG. 4B, as well asFIG. 5C.

A collecting lens 76 collimates and directs the radiation fromoptoelectronic elements 70 through one or more patterning elements 78.The patterning elements cause the radiation from elements 70 to beprojected onto the scene in a predefined pattern, which is detectable inthe electronic image formed by imaging assembly 28. This pattern in theimage is processed in order to compute the depth map of the scene.Patterning elements 78 may comprise a patterned transparency, which maycomprise a micro-lens array (MLA), as described, for example, in theabove-mentioned U.S. 2008/0240502 or WO 2007/105205, and/or one or morediffractive optical elements (DOEs), as described in U.S. PatentApplication Publication 2009/0185274, whose disclosure is alsoincorporated herein by reference. Additionally or alternatively, whenelements 70 emit coherent radiation, patterning elements 78 may comprisea diffuser, which casts a laser speckle pattern on the scene.

Each of optoelectronic elements 70 emits radiation that forms arespective stripe 80, 82, 84, . . . , as shown in FIG. 4B. (Although thefigure shows six such elements and respective stripes, a larger orsmaller number of elements and stripes may be used, depending onapplication requirements.) Reflector 74 may be slightly curved, as shownin the figure, so that the stripes spread over a wider area and overlapthe adjacent stripes at their edges. As explained above, controller 31(FIG. 1) activates elements 70 to emit radiation sequentially, insynchronization with the rolling shutter of image sensor 38, during eachimage frame captured by imaging assembly 28. Thus, each region of thescene is illuminated during the exposure periods of the correspondingrows of sensor elements 40.

In embodiments in which patterning elements 78 comprise a MLA or othertransparency, each stripe 80, 82, 84, . . . , passes through adifferent, respective region of the transparency, and thus creates arespective part of the overall illumination pattern corresponding to thepattern embedded in the transparency. Projection optics 34 projects thispattern onto the object.

On the other hand, in embodiments in which patterning elements 78comprise a DOE, either lens 76 or one of elements 78 (or the geometry ofoptoelectronic elements 70) is typically configured to create anappropriate “carrier” angle for the beam emitted by each of theoptoelectronic elements. In such embodiments, the beams emitted by thedifferent optoelectronic elements use different parts of lens 76, whichmay therefore be designed so that the collimated beams exit atrespective angles corresponding to the desired vertical fan-out.Alternatively, the illumination module may comprise some other type ofoptics, such as a blazed grating with as many different zones as thereare optoelectronic elements.

Further details of the fabrication of illumination module 32, as well asother, similar sorts of modules, are described in the above-mentionedU.S. Provisional Patent Application 61/300,465.

FIGS. 5A and 5B are schematic side and top views, respectively, of anoptoelectronic subassembly 90, while FIG. 5C is a schematic pictorialview of a prism 92 used in subassembly 90, in accordance with anotherembodiment of the present invention. Subassembly 90 may be used in placeof the corresponding components in module 32.

Optoelectronic subassembly 90 comprises a row of edge-emittingoptoelectronic elements 70, such as laser diodes, which may befabricated on a suitable substrate as in the preceding embodiment. Insubassembly 90, however, the radiation emitted by elements 70 isreflected internally from an interior surface 94 (typically with asuitable reflective coating) of prism 92. The radiation from elements 70enters prism 92 via a curved entry surface 96. As a result, respectivebeams generated by elements 70 spread apart and overlap partially withthe adjacent beams. Controller 31 actuates elements 70 to emit radiationsequentially during each image frame in synchronization with the rollingshutter of image sensor 38

Illumination Module With Surface Emitters

FIG. 6 is a schematic side view of an illumination assembly 100, inaccordance with an alternative embodiment of the present invention.Assembly 100 may be used in system 20 in place of illumination assembly22. Assembly 100 comprises radiation sources in the form of atwo-dimensional matrix of optoelectronic elements 110, which arearranged on a substrate 102 and emit radiation in a directionperpendicular to the substrate. Although FIG. 6 shows only a single row114 of elements arrayed along the X-axis, assembly 100 actuallycomprises multiple, parallel rows of this sort, forming a grid in theX-Y plane. FIG. 6 illustrates an 8×8 grid, but larger or smallermatrices, not necessarily square or rectilinear, may alternatively beused.

In contrast to the preceding embodiments, elements 110 comprisesurface-emitting devices, such as light-emitting diodes (LEDs) orvertical-cavity surface-emitting laser (VCSEL) diodes, which emitradiation directly into the Z-direction. An array of microlenses (orother suitable micro-optics, such as total internal reflection-basedmicro-structures) 112 is aligned with elements 110, so that a respectivemicrolens collects the radiation from each element and directs it intoan optical module 104. The optical module comprises, inter alia, asuitable patterning element 106, as described above, and a projectionlens 108, which projects the resulting pattern onto the scene.

FIG. 7 is a schematic representation of a portion of an image frameilluminated by assembly 100, in accordance with an embodiment of thepresent invention. Each microlens 112 spreads the radiation from thecorresponding optoelectronic element 110 over a region of the scene thatcorresponds to a group of pixels 44. (Typically there is some overlapbetween neighboring regions, as in the preceding embodiments.) Elements110 are arranged in multiple rows 114, 116, . . . . In typicaloperation, controller 31 actuates all the optoelectronic elements ineach row in turn in synchronization with the rolling shutter of imagesensor 38, in accordance with the scheme shown in FIG. 3, for example.Thus, as described above, the area of each pixel 44 is illuminatedduring the exposure period of the corresponding sensor element 40.

Although the above embodiments are described, for the sake of clarity,in the context of system 20 and certain specific geometricalconfigurations of illumination and sensing, the principles of thepresent invention may similarly be applied in systems and configurationsof other sorts.

Synchronization Over Multiple Sensors

FIG. 8 is a schematic side view of an imaging system 120, in accordancewith another embodiment of the present invention. In this system, asynchronization controller 121 synchronizes the operation of multiplesensing units 122, 124, 126, 128. Each of these sensing units typicallycomprises an illumination assembly and an imaging assembly, whichoperate in concert as in system 20. Each sensing unit 122, 124, 126, 128projects a respective patterned beam 132, 134, 136, 138 onto a scene 130and forms a respective image of the part of the scene that isilluminated by the respective pattern.

In order to cover scene 130 completely, the projected patterned beamstypically overlap in overlap regions 140. In conventional operation, theoverlap of the patterns could lead to inability of sensing units 122,124, 126, 128 to detect their own patterns reliably in regions 140 andthus to loss of 3D information in these regions. One way to overcomethis problem could be to operate the sensing units at differentwavelengths, so that each unit senses only its own pattern. Thissolution, however, can be cumbersome and require costly optoelectronicsand optical filters.

Therefore, in system 120, controller 121 controls the timing of theillumination assemblies and the rolling shutters of the imagingassemblies in sensing units 122, 124, 126, 128 so as to control theoverlap between the regions that are illuminated at any given time.Typically, the sensing units are controlled so that they illuminate andcapture radiation from respective non-overlapping stripes 142, 144, 146,148. Within each sensing unit, the illumination stripe and the sensingarea that is triggered to receive radiation by the rolling shutter areinternally synchronized as described above. Furthermore, the timing ofall the sensing units is coordinated to avoid interference. Thus, forexample, all of the sensing units simultaneously activate theirrespective stripes 142, followed by stripes 144, and so on, so that nomore than a single sensing unit is active within each overlap region 140at any given time. Each sensing unit provides 3D mapping data withrespect to its own part of scene 130, and a processing unit (such ascontroller 121 or another computer) stitches the data together into acombined depth map.

The scheme illustrated in FIG. 8 is just one example of a possiblesynchronization pattern, and alternative geometrical and timing patternsmay also be implemented to achieve similar objectives. For example, thesynchronized sensing units may be arranged in a two-dimensional array inorder to cover a wider area of scene 130. Depending on the geometricalarrangement and the timing of the sensing units, systems of multiplesynchronized sensing units may be used to capture depth information overgreater areas of substantially any desired size and profile, or,alternatively or additionally, with greater speed.

Alternatively, sensing units 122, 124, 126, 128 may operate togetherwithout a centralized controller to regulate synchronization. Forexample, each sensing unit may adjust its own timing so as to maximizeits depth readings. Thus, the entire system will converge to an optimalsynchronization. Additionally or alternatively, the sensing units maycommunicate with one another using a token ring type protocol, withoutcentralized control.

FIG. 9 is a schematic pictorial view of an imaging system 150, inaccordance with yet another embodiment of the present invention. Thisembodiment is similar in its principles of operation to the embodimentof FIG. 8: Multiple sensing units 152, 154, . . . , project respectivepatterned beams 156, 158, . . . , onto a scene, while controlling thetiming of their respective illumination assemblies and rolling shuttersso as to illuminate and capture radiation from respective sequences ofstripes 160. Beams 156 and 158 overlap in an overlap region 162.Although for the sake of simplicity, only two sensing units are shown inFIG. 9, any suitable number of sensing units may be arranged in thismatter.

In system 150, however, sensing units 152 and 154 and their beams 156and 158 are offset from one another in a direction perpendicular to thescan direction of the illumination and rolling shutter (horizontaloffset with vertical scan in the view shown in FIG. 9), as opposed tothe parallel offset shown in FIG. 8. Therefore, most or all of stripes160 may overlap with certain stripes of the neighboring sensing unit.The scans of sensing units 152, 154, . . . , are therefore synchronizedso that each stripe is illuminated in different time periods from itsoverlapping neighbors. As shown in FIG. 9, there is no need for preciseoverlap between stripes 160 of the different sensing units, nor do thestripes need to be exactly parallel. Generally speaking, the sensingunits may be arranged in any desired arrangement, as long as thesynchronization schedule can make overlapping stripes disjoint in time.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsubcombinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

The invention claimed is:
 1. Optical apparatus, comprising: a pluralityof radiation sources, mounted on a substrate and configured to emitoptical radiation; a patterning element, comprising a transparency;collection optics, comprising an array of micro-optics, which arealigned with the radiation sources so that a respective micro-opticcollects the radiation emitted by each of the radiation sources anddirects the radiation toward the patterning element, while causing theoptical radiation emitted by each of the radiation sources to passthrough a different, respective region of the transparency so as to formdifferent, respective patterns; projection optics, which are configuredto project the patterns of the radiation from the patterning elementonto a scene; an imaging assembly, comprising an image sensor andobjective optics configured to form an optical image of the scene on theimage sensor, so that the image sensor forms electronic images of thescene; and a controller, which is coupled to actuate the radiationsources sequentially in a pulsed mode, so as to form the different,respective patterns in succession, and to analyze the patterns in theelectronic images so as to generate a depth map of the scene byanalyzing multiple images, generated in succession by the image sensor,containing the different, respective patterns formed due to emissionfrom each of the plurality of radiation sources.
 2. The apparatusaccording to claim 1, wherein the transparency comprises a micro-lensarray.
 3. The apparatus according to claim 1, wherein the image sensorcomprises an array of sensor elements arranged in multiple groups, whichare triggered by a rolling shutter to capture the radiation from thescene in successive, respective exposure periods from different,respective areas of the scene, and wherein the controller is coupled toactuate the radiation sources in synchronization with the rollingshutter.
 4. The apparatus according to claim 1, wherein the radiationsources comprise a matrix of light-emitting elements, which are arrangedon the substrate and are configured to emit the radiation in a directionperpendicular to the substrate.
 5. The apparatus according to claim 1,wherein the radiation sources comprise a row of edge-emitting elements,which are arranged on the substrate and are configured to emit theradiation in a direction parallel to the substrate.
 6. The apparatusaccording to claim 5, wherein the collection optics comprise a reflectordisposed on the substrate so as to turn the radiation emitted by theedge-emitting elements away from the substrate and toward the patterningelement.
 7. The apparatus according to claim 6, wherein the reflectorcomprises a prism.
 8. A method for imaging, comprising: arranging aplurality of radiation sources on a substrate so as to emit opticalradiation; directing the radiation emitted by the radiation sourcestoward a patterning element, comprising a transparency, using an arrayof micro-optics that are aligned with the radiation sources so that arespective micro-optic collects the radiation emitted by each of theradiation sources so as to cause the optical radiation emitted by eachof the radiation sources to pass through a different, respective regionof the transparency, thus forming different, respective patterns;projecting the patterns of the radiation from the patterning elementonto a scene; actuating the radiation sources sequentially in a pulsedmode so as to form the different, respective patterns in succession;forming an optical image of the scene on an image sensor, so that theimage sensor forms a succession of electronic images of the scenecontaining the different, respective patterns formed due to emissionfrom each of the plurality of radiation sources; and analyzing thepatterns in the succession of electronic images so as to generate adepth map of the scene, wherein analyzing the patterns comprisesanalyzing images containing the different, respective patterns formeddue to emission from each of the plurality of radiation sources insuccession.
 9. The method according to claim 8, wherein the transparencycomprises a micro-lens array.
 10. The method according to claim 8,wherein the image sensor comprises an array of sensor elements arrangedin multiple groups, in which the groups of the sensor elements receivethe radiation from different, respective areas of the scene, wherein themethod comprises triggering the groups of the sensor elements with arolling shutter to capture the radiation from the scene in successive,respective exposure periods so as to form the electronic image of thescene, and wherein actuating the radiation sources sequentially in thepulsed mode comprises operating the radiation sources in synchronizationwith the rolling shutter.
 11. The method according to claim 8, whereinthe radiation sources comprise a matrix of light-emitting elements,which are arranged on the substrate and are configured to emit theradiation in a direction perpendicular to the substrate.
 12. The methodaccording to claim 8, wherein the radiation sources comprise a row ofedge-emitting elements, which are arranged on the substrate and areconfigured to emit the radiation in a direction parallel to thesubstrate.
 13. The method according to claim 12, wherein arranging theplurality of the radiation sources comprises providing a reflector onthe substrate so as to turn the radiation emitted by the edge-emittingelements away from the substrate and toward the scene.
 14. The apparatusaccording to claim 13, wherein the reflector comprises a prism.
 15. Theapparatus according to claim 1, wherein the micro-optics comprisesmicrolenses.
 16. The method according to claim 8, wherein themicro-optics comprise microlenses.